CPAP for Preoxygenation

In a patient with shunt, CPAP is needed for preoxygenation. In my ED, we make this happen with the ventilators installed next to every resuscitation bed.

However, not every ED has ventilators readily available and it might take >15 minutes to have respiratory bring a NIV machine or a vent. In that case, you want to use a BVM with a PEEP valve.

PEEP Valve Fits on any BVM

However, this device provides CPAP only when the patient is expiring. In a patient who is not breathing rapidly, most of the cycle will be spent at zero PEEP. Once the patient is apneic, the device won’t supply PEEP unless you manually give ventilations–even then the PEEP will only be there immediately following the ventilation. However, if you add a constant source of flow, like a nasal cannula set to 15 lpm then the BVM/PEEP Valve combo will give continuous PEEP regardless of the patients resp rate or even when they become apneic. In the following video, a PEEP valve set to 10 cm H20 provides between 6-8 cm H2) of PEEP throughout the cycle. This same nasal cannula should be on the patient anyway for apenic oxygenation and NO DESAT (Nasal Oxygen During Efforts Securing A Tube) during the intubation procedure.

PURPOSE: Hypoxemia during airway management remains an important cause of morbidity and mortality. Oxygenation during intubation via nasal prongs may prevent critical desaturations (Anesthesiology 1988, J Korean Med Sci 1998). We evaluated the effectiveness of oxygen administration via nasal prongs during apneic period following induction of general anesthesia.

METHODS: We conducted a randomized, controlled, double-blind study in patients without significant cardiac or respiratory disease undergoing elective surgery (age 18-65, ASA I-III). Patients randomly received oxygen via nasal prongs at 0, 5, or 10 L/min. Following preoxygenation, general anesthesia was induced. At 90 seconds after induction, nasal prongs were applied and oxygen was delivered according to the experimental group. At 4.5 minutes post-induction the patients were intubated.

RESULTS: The final study population consisted of 41 individuals, with 14 in the 0 L group, 13 in the 5 L group, and 14 in the 10 L group. The mean values are 134 ± 75, 168 ± 138 and 253 ± 146 mmHg respectively. A statistically significant difference was demonstrated between the three treatment protocols (p=0.030), across time (p=0.028), and in the treatment effect across time (p=0.017). Mean PaO2 was higher in the 10 L group (p=0.001) than the 5 L group and 0 L group at 4.5 minutes (p=0.004). CONCLUSIONS: Apneic oxygenation with 10 L/min compared to 5 Lmin via nasal prongs demonstrated delay of desaturation and maintenance of higher PaO2 levels during elective intubation.

CLINICAL IMPLICATIONS: Nasal prongs are available in all of the patient care areas; therefore this simple, benign, inexpensive technique may be useful as a routine addition to airway management.

PMID: 24154362

ApOx and Shunt Physiology

This article lends credence to the point that patients with shunt physiology either preexisting for during apnea will not benefit to same extent (Anesthesiology 1973;39(6):588)

Nasal Cannula to Augment Face Masks (as Rich and I advocate)

The presence of a facemask leak significantly reduces the effectiveness of pre-oxygenation and increases the risk of post-induction hypoxia. We randomly assigned 24 healthy volunteers to a six-period crossover trial with and without a simulated facemask leak. Pre-oxygenation was performed using a standard anaesthesia machine circuit supplemented either by nasal prong oxygen or by anaesthesia machine flush oxygen. Each intervention was completed with both 3-min tidal breathing and 8 deep breath techniques: end-tidal oxygen fraction was used as the measure of pre-oxygenation effectiveness. The presence of a stimulated mask leak significantly reduced the effectiveness of pre-oxygenation regardless of the breathing method used. With a simulated facemask leak introduced, the mean (SD) end-tidal oxygen fraction with the 3-min tidal breath technique was 74.7 (9.3)% compared with 57.5 (6.2%) for the 8 deep breath technique with 3-min tidal breathing and a leak. End-tidal oxygen fractions increased by 11.0% (95% CI 7.8–14.3%) (p < 0.0001) with the addition of nasal prong oxygenation and 16.8% (13.6–20.0%) (p < 0.0001) with machine oxygen flush compared with standard pre-oxygenation. When a leak is present, 3-min tidal breathing with either nasal prong or anaesthesia machine flush oxygenation is an effective pre-oxygenation method, and preferable to the 8 deep breath method.

Hi, I think that might be wrong. O2 flows through the one way valve constantly- this can be felt and heard when checking the BVM.
When the patient inspires the flutter valve will open further and they will draw in O2 from the bag and reservoir, providing there is a good seal.

In the breathing patient, which is the more effective oxygen delivery method:
1. Commercial CPAP device (Flow-safe, Boussingnac)
2. BVM with PEEP
I assume the combination BVM/PEEP with Nasal Prongs is better than above but requires 2 sources of O2.
George

It was nice to be able to cite (after the fact) anaesthetic literature (via your article) to an anaesthetist who tried to tell me that nasal cannula oxygenation would not be helpful during a high risk RSI.
🙂

Scott,
Just clarification, but if we’re using an LTV1200 for CPAP during PreOx, it would be easier to continue using the vent during ApOx? If in a situation where you have NIV capabilities, one could leave the mask on, and just switch to A/C to use the vent while patient is apneic, right?

Lee, Sorry I missed this comment originally. You still need the nasal cannula for even vented apneic ox as the vent will not pick up the small O2 utilization as a breath. But a vent set to PEEP or a very low RR with a NC underneath would work wonderfully.

Scott, excellent, … great tips regarding oxygenation, thank you. A word re the use of NIV during the apneic period. The LTV 1200 that Lee is using does provide a continuous bias flow of O2 at 10 lpm and will maintain CPAP (as long as the conserve O2 feature is “off”) whether the patient is spontaneouly breathing or apneic. The addition of NC may not add any advantage as the ventilator will maintain constant CPAP by adding gas flow at whatever FiO2 is set on the ventilator. NIV devices that I am familiar with all behave this way.

Thanks for the information. Where I trained (Australia and UK) we have always prexoygenated with BVM. The cited superiority of high flow NRM over BVM actually refers to an abstract on the internet and the article written by Dr Weingart (1) does state without reference that standard flow meters are capable of achieving very high flows in the order of 30-60 l/min if dialled right up. The data presented in the reference (abstract form on net) shows NRM achieving 77-89% at 30-60l/min respectively (and not greater than 90% as stated). Iis there any data to support these higher flow rates are achievable with standard flowmeters as would have to have a 60 l/min flow rate to achieve the higher FiO2? Otherwise if you were contemplating this technique a high flow (=expensive) flowmeter would be needed and then would achieve up to 89% if data cited was accurate and verifiable. I think overall this article is excellent but do have these doubts about NRB for preoxygenation. Nasal oxygen would improve things of course and perhaps the combination if better than BVM with inadequate seal.
1. Earl JW. Delivery of high FiO2. from http://www.rcjournal.com/abstracts/2003/?id=OF-03-257.
2. Weingart SD, Levitan RM. Preoxygenation and prevention of desaturation during emergency airway management. Ann Emerg Med. 2012;59:165-75.e1.

Today I had the opportunity to visit our biomedical equipment division. I tested a standard (15l/min) flow meter with a Fluke VT mobile gas flow analyzer. The calibrated flows on the wall flow meter were accurate. When the valve was fully opened past 15 l/min it only generates a maximum 19l/min flow.
May be the flow meters are different pressures in the USA ( I work in Australia). But the flow meters I checked would not produce the required flow rates to achieve FiO2 > 90% with NRB mask alone.

Is there a benefit to using the nonrebreather on its own at 30-60 lpm as opposed to using the nonrebreather at 15 lpm plus the use of nasal cannula to the max? I’ve been reading Dr. Levitan’s NO DESAT material, which recommends nonrebreather plus nasal cannula…

The NRB should ALWAYS be put up as high as your flowmeter will allow. NC adds little to this, but there is no reason not to put it on at 15 lpm right at the start if you have enough flowmeters. When using oxygen tank (limited to 15 lpm) with the NRB, there is prob. an advantage to NC in addition. Dr. Levitan was my co-author on the paper recommending always try to get 30-40 lpm with NRB.

I have read your articles referenced above including the joint article with Levitan and they were excellent.
question re Pre-Ox:
– While the patient is spontaneously breathing before you push your drugs? What is the advantage of using the NRB mask over the BVM with good seal? If the patient is taking adequate breaths surely the NRB is delivering higher FiO2 unless you have flow valves that open up to 30L-60L per min where they may be equivalent? So essentially I’m trying to figure out when NRB mask is going to be better than NRB with good seal (not just equivalent to) and why you recommend using it for Pre-Ox?

question re Ap-Ox
– if the patient is not breathing, does the NRB bag provide any oxygen to the patient? If the mouth is closed, Is this via the nasal route into the pharynx? Therefore if nasal cannula are already in place does the NRB offer any additional advantage to being on the patient’s face, especially if the mouth is closed?

most BVMs provide only room air to spont. breathing pts as the exhalation valve is where they are exchanging gas. even in the rare, more expensive bags that have a 1-way valve on exhalation, you need to maintain perfect seal for high fio2.

thanks Scott -1 follow up questions to help me get my head around this and 2 others:

1. So because BVM’s exhalation port does not have 1 way valve then during spontaneous breathing entrain a mixture of room air through this port and 100% 02 from the bag through the inspiratory port (that opens through the negative pressure of the spontaneous breath.
With the NRB you are also getting a mixture of entrained air from room air (through the holes on the mask) and 100% O2 through the reservoir.

So why then does the NRB provide the patient much better FiO2 than the BVM when both devices are providing a mixture of room air and 100% 02?

2. Do you think apnoeic oxygenation would be optimised by having pre-placed nasopharyngeal airways that you insert your nasal prongs into to improve airflow to the oropharynx?

3. Do you find the tubing from nasal prongs interferes with the tight seal you need to obtain when using a BVM or the mask attached to a NIV machine?

Scott, when using the NRB for PreOx prior to intubation, can you substantially improve your Fi02 by taping the expiration ports that are NOT covered with 1 way valve. I understand these ports without valves are there to prevent suffocation in the event your oxygen runs out. However if you are only using this NRB temporarily for 3 minutes with you continuously attending the patient prior to intubation to improve FiO2 the benefits would probably outweigh the risks.
What are you thoughts? Have you tried this?

Have you had much experience with the Mapleson C devices for preoxgenation. Apparently quite good but needs some additional training to use in respect to setting the oxygen flow rate and the bag not being self inflating.
Also useful for manual ventilation, can provide PEEP and can allow you to feel the compliance of lungs. Also makes it easy to provide gently manually supported spontaneous breaths as can feel when patient inspires.
Compared with BVM and NRB seems like the only device that can easily be used in ED for BOTH spontaneously breathing Preox AND manually ventilating Reox. I wonder whether we should be moving towards this as an all in one solution. Rarely seen in ED in my area currently unless brought to the party by the anaesthetist. Also I have no idea if pricey or not.

sure. Though since you’ve opened my eyes to this BVM issue, I do wonder though if the BVM even with PEEP valve is really giving the patient 100% Fi02 if there are even small leaks around the mask. I haven’t yet tested with the PEEP valve but do have some BVM’s with a one way valve on the expiratory port (they must be affordable here as my dept has a bunch of disposable ones) and I wonder whether the patient is getting much ventilation with spont breaths given how much effort is required to open the inspiratory valve – tried it on myself with a good mask seal and found with nasal breathing the inspiratory valve only opening slight amounts and feeling like I was suffocating.

Obviously as you describe nasal cannula assist during ApOx.
However during the PreOx phase, if you use a NRB with O2 flow turned up to max above 15L/min 02, does the addition of Nasal Cannula even at 3-5L/min increase your FiO2 significantly? The semi awake patient may only tolerate those type flows from Nasal Cannula before pushing sedation so wondered if this is improving FiO2 by creating an O2 reservoir in the pharyx (at the end of expiration just before inspiration). Do you know of any research demonstrating an increase in FiO2 with such a NRB + Nasal Cannula combo?

I understand the PAP, but when you demonstrated the BVM/PEEP with the NC, you had a change in pressure. You were showing a pressure of approx. 5 cm/H2O on inspiration and 10 cm/H2O on expiration. So why would this not be considered BiPAP? This would be very handy in EMS where access to BiPAP is limited due to equipment cost.

I presume it is CPAP where due to your equipment you are not getting less than ideal pressure provided in inspiration i.e the inspiratory pressure is less than the expiratory pressure instead of being the same. Effectively it is PEEP with a little of pressure during inspiration as well (provided by adding the continuous oxygen flow via the nasal cannula).

BIPAP would have a greater inspiratory pressure than expiratory pressure i.e the 10 and 5 would be the other way round.

A question from a basic level provider (asking for educational reasons).
Is the use of a peep valve for re-oxygenation (or BVM ventilation if the pt is hypoxemic on high FiO2) still safe in PTS with a head injury w/ suspected increased ICP?

I’m not a neuro guy (and am not an als/ccp provider) so I don’t know if the possible negative effects PEEP has on the CPP (CPP=MAP-ICP) outweigh the need to oxygenate the pt.

I’ve been using pre-oxygenation via NC since I heard you talk about it – but I keep running into a “Style-point” roadblock – the RT’s always want to argue about the flow rate on the NC, saying it “can’t deliver above 5L…” I tried to explain the difference between apneic oxygenation and the actively breathing person to no avail. Are there any quick explanations you could offer? Maybe an in-service is indicated.

PURPOSE: Hypoxemia during airway management remains an important cause of morbidity and mortality. Oxygenation during intubation via nasal prongs may prevent critical desaturations (Anesthesiology 1988, J Korean Med Sci 1998). We evaluated the effectiveness of oxygen administration via nasal prongs during apneic period following induction of general anesthesia.

METHODS: We conducted a randomized, controlled, double-blind study in patients without significant cardiac or respiratory disease undergoing elective surgery (age 18-65, ASA I-III). Patients randomly received oxygen via nasal prongs at 0, 5, or 10 L/min. Following preoxygenation, general anesthesia was induced. At 90 seconds after induction, nasal prongs were applied and oxygen was delivered according to the experimental group. At 4.5 minutes post-induction the patients were intubated.

RESULTS: The final study population consisted of 41 individuals, with 14 in the 0 L group, 13 in the 5 L group, and 14 in the 10 L group. The mean values are 134 ± 75, 168 ± 138 and 253 ± 146 mmHg respectively. A statistically significant difference was demonstrated between the three treatment protocols (p=0.030), across time (p=0.028), and in the treatment effect across time (p=0.017). Mean PaO2 was higher in the 10 L group (p=0.001) than the 5 L group and 0 L group at 4.5 minutes (p=0.004).

CONCLUSIONS: Apneic oxygenation with 10 L/min compared to 5 Lmin via nasal prongs demonstrated delay of desaturation and maintenance of higher PaO2 levels during elective intubation.CLINICAL IMPLICATIONS: Nasal prongs are available in all of the patient care areas; therefore this simple, benign, inexpensive technique may be useful as a routine addition to airway management.

Scott,
When you see the O2% bumping up from say, 90% range all the way up to 100% just by adding 5cm/h20 of CPAP (obviously maxed at 100 % FIO2).. do you go up to 10 on CPAP- or all the way up to 15 on CPAP, since we want to optimize Pao2, and 100% could mean Pao2 of 90 or… 400?

Hey Scott,
It seems as though whether Pa02 truly directly feeds the hemoglobin saturation directly, or if it’s just a marker of optimization of the things you speak about (alveolar recruitment, de-nitrogenation, etc.), higher PaO2 levels appear to correlate with and are associated with a longer safe-apenic period. This was a small study but just an example:

Therefore, it seems additional increases in CPAP(PEEP), (in pts refractory to 100% supplemental O2) may be a valuable method of increasing the safe apenic period, by increasing PaO2 to higher levels despite a pulse ox of 100% at a given lower level of CPAP.

Dear Scott,
In trying to wrap my head around the concept of bag-valve mask ventilation and PEEP, I ask if you could please just follow my logic and way of thinking and see where I may be losing any concept, or where my logic may be going stray…

I mentally break down the entire cycle into 3 parts:

1. Inspiration
2. Expiration
3. *the period between breathes

1. Inspiration- When the patient takes a breath, I would assist his/her ventilation by gently squeezing the bag with a tight seal, and therefore supplying PEEP during inspiration.

2. Expiration- During expiration, by adding the PEEP valve, I can obtain PEEP during this phase as well (I guess by creating some sort of resistance?).

3. During the periods between breathes (more prominent when the pt is not tachypneic), benefit of continued positive pressure would be to keep the alveoli open during this time, allowing an easier time for the next inspiration, and with a BMV+PEEP Valve, this can only be done by placing additional continuous flow, of O2NC @15L/min.

Questions I have are:

1. Can you explain the mechanism of adding nasal cannula with the PEEP valve? Is it simply that the nasal cannula at 15L/min is providing its own intrinsic mechanism of some PEEP?… or is the continuous PEEP a result of some sort of interaction with the PEEP valve?

2. In your video, you are taking spontaneous breaths without bagging- so when you add NC, you get two different PEEPS (one all the time, and then a little higher during expiration… interesting concept- sorta like reverse BIPAP) .. if you’re assisting the pts ventilations ANd using 15L/min NC, are we then getting a 3 different sets of CPAP pressures- one during inspiration, one during expiration, and one during the time in between?

3. Are we actually also getting some apneic oxygenation in there during the period between the breaths?

Thanks so much in advance for taking the time to answer all these questions we all perpetually bombard you with!

Flow is everything. Normal insp flow is approx 40 l\m, coming out of a Flow meter one can achieve upwards of over 100 l\m with the knob turned OPEN, clearly meeting or EXCEEDING normal insp flow to achieve 100% 02 DELIEVERED prior to intubation via a MASK, the use of a nasal cannula at 15 l/m during intubation would then AUGMENT any 02 HgB saturation gain with this mask. To me this is the QUICKEST and SIMPLEST way to achieve the GOALS of no or minimal desaturations and buy some extra TIME for intubation and avoid the possibility of aspiration if a second attempt is needed.

A NC at 10 Lpm will provide only 1 cmH20 of cpap. This is why Nasal High Flow Cpap works so well. If you are giving the patient 60 Lpm, they are getting 6 cmH20 of Cpap. I use NHF all the time where I work at for many issues and it’s a standard practice to have a patient on 60-to-50 Lpm and 100%-to-35% of Fi02.

Trackbacks

[…] ill obese patients before and during rapid sequence intubation. Find out how to do this at EMCrit.org — Preoxygenation, reoxygenation, and deoxygenation.Weingart SD, Levitan RM. Preoxygenation and Prevention of Desaturation During Emergency Airway […]

[…] his patients as part of RSI on EMRAPTV using an LMA.EMCrit.org has a great page of resources on preoxygenation, reoxygenation and deoxygenation. The Scott Weingart approach to ‘delayed sequence intubation’ is described in Emcrit […]

[…] his patients as part of RSI on EMRAPTV using an LMA.EMCrit.org has a great page of resources on preoxygenation, reoxygenation and deoxygenation. The Scott Weingart approach to ‘delayed sequence intubation’ is described in Emcrit Podcast […]

[…] been getting more publicity. In particular, Scott Weingart of EMcrit and Richard Levitan recently published a paper comprehensively describing its use in difficult intubations. They advise placing a cannula at 15 […]

[…] during tracheal intubation. Videos of the techniques described in this article can be found at http://emcrit.org/preoxygenation. Supervising editors: Gregory W. Hendey, MD; Donald M. Yealy, MD Fundingandsupport: By […]

[…] us had had formal teaching on such a scenario, but the application of various lessons (EGDT, DSI, apnoeic oxygenation) served us well on the night & truly made a difference to this patients outcome […]

[…] less effective oxygen delivery devices, this also has benefits of providing CPAP (as explained by Scott Weingart on the EMCrit website) when used in combination with a PEEP valve and a mask capable of creating a seal, as well as […]

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Hi, my name is Scott Weingart. I am an ED
Intensivist from New York. Along with my friends, we are attempting to provide and teach Maximally Aggressive Care, Everywhere! From the field to the ICU, EMCrit is about optimal critical care and resuscitation.